The invention relates to a vehicle wheel for a double-track vehicle or an external cover therefor, having passage openings, particularly for a cooling air flow for a wheel brake provided on the interior side of the wheel, in the lateral projection. The passage openings have a width in the radial direction, which changes when viewed in the rotating direction of the wheel. With respect to the technical environment, reference is made by way of example only to German patent document DE 42 31 082 A1.
Measures for reducing drag, particularly at higher driving speeds, are becoming increasingly significant on two-track vehicles. In this case, the term “drag reduction” should be understood in the broadest sense. Here, it is a priority to search for measures which reduce the fuel consumption particularly on free-moving motor vehicles. With respect to the above, the vehicle wheels or their influence on the drag also should be considered, in which case a full-surface lateral cover of the wheel house (or at least of the wheel) would naturally be the best. However, on the other hand, a cooling air flow for a wheel brake provided on the interior side of the wheel has to be guaranteed. Accordingly, passage openings in the wheel disk, or a cover mounted on the latter or, in the case of a spoke wheel, between these spokes, as a rule, cannot be eliminated. In principle, it is known in this case to design these passage openings while taking into account flow dynamics such that a favorable above-mentioned cooling air flow can occur. For this purpose, the passage openings may, in the lateral projection, have a changing width in the radial direction when viewed in the rotating direction of the wheel.
A further improvement with respect to a vehicle wheel or a cover therefor, of the above-mentioned type is provided by which, in the broadest sense, a reduction of the drag can be achieved.
The solution of this task is characterized in that, viewed against the rotating direction of the wheel when the vehicle is traveling forward, the above-mentioned width decreases, and in that the centers, viewed in the radial direction, of the virtual segments of the passage opening following one another against the rotating direction move virtually in the direction of the wheel center. In this case, the passage openings may preferably be bounded by spokes extending essentially in the radial direction.
Although this suggested measure does not directly reduce the drag but rather the moment of resistance directed against a wheel rotation and resulting from aerodynamic forces and the wheel rotation, as will be explained in detail below, this measure leads to a measurable reduction of the fuel consumption.